merge revision(s) 39812: [Backport #8147]

	* gc.c: Improve accuracy of objspace_live_num() and
	  allocated/freed counters. patched by tmm1(Aman Gupta).
	  [Bug #8092] [ruby-core:53392]


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_0_0@40168 b2dd03c8-39d4-4d8f-98ff-823fe69b080e